How to wait for an operation - to another operator - to complete within an operator (import_scene)
Path of least resistance. this works but it's hardly programmatically sound. if anyone has nay other functioning solutions i'm all ears :)

sceneobjects = 0
currentobjects = 0

def modal(self, context, event):
    if self.currentobjects &gt; self.sceneobjects:
        bpy.ops.object.select_all(action='DESELECT')
        print("finished")
        return {'FINISHED'}
    else:
        self.currentobjects = len(bpy.data.objects)
        print(context.window_manager)
        return {'PASS_THROUGH'}

def invoke(self, context, event):
    #save current number of objects on scene
    self.sceneobjects = len(bpy.data.objects)
    #start the import
    bpy.ops.import_scene.fbx("INVOKE_REGION_WIN")
    context.window_manager.modal_handler_add(self)
    return {'RUNNING_MODAL'}